The Central Mountain Range of Taiwan Island in Central Weather Bureau Non-hydrostatic Limited Area Model

The mountains of Taiwan affect both the airflow and mesoscale weather systems impinging on the island significantly since two-thirds of the land-mass of the country is covered by rugged terrain. The orographic feature which has the most significant impact on atmospheric systems is the Central Mountain Range(CMR) which runs through Taiwan in a NNE-SSW direction with a width of about 120km, a length of about 300km and an average height of 2km. The dominant peak of the CMR has a height of 3997m above the mean sea level. Since Taiwan is surrounded by oceans, it provides a unique environment for studying the orographic effects on prevailing airflow and impinging mesoscale weather systems.

The non-hydrostatic forecast system(NFS) of Taiwan Central Weather Bureau(CWB) have operational since 1999, which have 0000UTC and 1200UTC two runs daily. NFS is 3-nested fourth order finite differencing model which have grids(grid size:45km/15km/5km, grid points:191x127, 145x139, 61x91), using split-explicit temporal integration scheme and Arakawa&Schubert(1974) cumulus scheme, Harshvardhan et al.(1987) radiation scheme, TKE E-£`planetary boundary layer parameterization scheme, and cloud water, cloud ice, rain water, snow such substances are included by the microphysics processes parameterization.

This article want to check the performances of CWB NFS, especially on several prominent weather problems related to the orographic effects of the topography of Taiwan, which includes: (a) local rainfall enhancement by the CMR on prevailing winds and mesoscale convective systems, (b) the formation of mesolows and mesocyclones, (c) the effects on Mei-Yu fronts, (d) the effects on mesoscale convective systems.